1. Field of the Invention
The present invention relates to a heat-radiating mechanism of a portable electronic apparatus, for example, a notebook-type personal computer. More specifically, the present invention relates to a heat-radiating structure.
2. Description of the Background Art
Referring to FIG. 7, a heat-radiating mechanism of a conventional portable electronic apparatus will be described by taking a notebook-type personal computer as an example. In notebook-type personal computers, a heat-radiating plate 53 made of copper or aluminum having a thickness from about 0.5 mm to 2.0 mm is tightly attached to a CPU 2, which is a heat-generating component mounted in a print wiring board 51 to release and radiate heat generated in the CPU 2 to the outside via a heat-radiating plate 53. When sufficient heat radiation is not expected with such a structure, a portion of the heat-radiating plate 53 is brought in contact with an aluminum keyboard supporting plate 6 on the back of the keyboard so that the heat in the CPU 2 is also radiated to the keyboard supporting plate 6.
However, metal such as copper and aluminum used for the heat-radiating plate 53 or the keyboard supporting plate 6 is highly rigid, and is hardly deformed by an external stress, thus its shape including its height is fixed. Furthermore, the CPU 2, the heat-radiating plate 53, and the keyboard supporting plate 6 are not completely smooth, because of, for example, fabrication tolerance or a change in shape over time or due to heat.
Therefore, when the height from the CPU 2 to the keyboard supporting plate 6 is structurally fixed, a space (clearance) is inevitably generated between the CPU 2 and the heat-radiating plate 53 and between the heat-radiating plate 53 and the keyboard supporting plate 6, so that they cannot be attached tightly to each other. This space functions as a contact thermal resistance between the CPU 2 and the heat-radiating plate 53 and between the heat-radiating plate 53 and the keyboard supporting plate 6, and prevents heat from moving, that is, being radiated, from the CPU 2 to the heat-radiating plate 53 and the keyboard supporting plate 6.
A space (clearance) between the CPU 2 and the heat-radiating plate 53 is referred to as “thermal conduction resistance space IS”. The distance in which the heat-radiating plate 53 is spaced apart from the CPU 2 is referred to as “resistance distance Dis”, and the area in which the thermal conduction resistance space IS is present in the direction parallel to the CPU 2 and the heat-radiating plate 53 is referred to as “resistance area Ais” (not shown). The size of the thermal conduction resistance space IS is referred to as “thermal resistance space size Vis”.
In order to reduce this contact thermal resistance, Japanese Laid-Open Patent Publication No. 2001-142574 discloses a method of providing a flexible thermal conductive member such as a heat-radiating grease 56 (not shown) or elastic heat-radiating elastomer 57 between the CPU 2 and the heat-radiating plate 53 and between the heat-radiating plate 53 and the keyboard supporting plate 6 to eliminate the thermal conduction resistance space IS. In this method, it is attempted to improve the heat transfer properties by replacing the air in the thermal conduction resistance space IS generated between the CPU 2 and the heat-radiating plate 53 and between the heat-radiating plate 53 and the keyboard supporting plate 6 with a flexible thermal conductive member or material having a larger thermal conductivity than that of air. In other words, the flexible conductive member in an amount corresponding to the thermal resistance space size Vis is filled in the thermal conduction resistance space IS.
In practice, each of the CPU 2, the heat-radiating plate 53 and the keyboard supporting plate 6 each exhibit a dimensional tolerance of 0.5 mm or more. Therefore, when the CPU 2, the heat-radiating plate 53 and the keyboard supporting plate 6 are brought in contact, they are spaced apart at a gap of 0.5 mm or more, and the thermal conduction resistance space IS is generated there. In other words, in order to eliminate the thermal conduction resistance space IS with a resistance distance Dis of 0.5 mm, it is necessary to fill with heat-radiating grease 56 or the heat-radiating elastomer 57 to a thickness of 0.5 mm or more. It is also necessary to determine the amount of the heat-radiating grease 56 or the heat-radiating elastomer 57 to be filled, in view of variation in the thermal resistance space size Vis of the thermal conduction resistance space IS due to thermal expansion or thermal contraction of the components caused in the process of absorbing and radiating heat from the CPU 2.
However, the thermal conductivity of the heat-radiating grease 56 or the heat-radiating elastomer 57 is larger than the thermal conductivity of air, but smaller than the thermal conductivity of copper or aluminum. Therefore, the heat transfer properties are poorer than when the CPU 2, the heat-radiating plate 53 and the keyboard supporting plate 6 are in direct contact. From this point of view, it is necessary to reduce the amount of the flexible thermal conductive member to be filled, that is, to reduce thermal conduction resistance space IS as much as possible. However, a slightly excessive amount of flexible thermal conductive member is provided to accommodate a change in the thermal resistance space size Vis of the thermal conduction resistance space IS.